Just wanted to post my positive results using a cheap USB->UART board. The "PL2303HX auto converter module" sells for US $2.31 including shipping. It does have 3V3 logic levels and works OK with my new R-Pi. http://www.ebay.com/itm/350568364250?ss ... 1439.l2649
I was able to use it to log in and work on the Pi, using the PuTTY terminal emulator on WinXP. http://www.chiark.greenend.org.uk/~sgtatham/putty/
This small USB-UART board comes with four F-F jumper cables to connect its header pins to the RPi GPIO pins. You only need to connect three wires: ground to ground, TxD to RxD, and RxD to TxD. Note this super-cheap board has a USB plug, not a socket, so it plugs directly into a PC, and the provided jumper wires are short. You may want to use a USB extender cable unless your RPi is actually taped to the side of your PC/Laptop/etc.
Then I realized I could go a step further, by disconnecting the microUSB power, and connecting the +5V line from the USB-UART chip to the RPi GPIO. It works! As long as you only need serial comms, this is all you need. The R-Pi in the photo is running (TP1-TP2 voltage shows 4.70 V) although it is not working on any big job.
Better quality photo: https://picasaweb.google.com/lh/photo/t ... directlink